The present invention relates to a chain tensioner particularly, but not exclusively, of the kind for maintaining tension in a transmission chain of an internal combustion engine.
In an internal combustion engine in which a chain is used to transmit driving power from the crankshaft to the camshaft, tension is conventionally imparted to the chain by means of a tensioner that comprises a piston that is biased out of a cylinder by means of hydraulic pressure, spring force or a combination thereof. A tensioning shoe is connected to the end of the piston and bears against the chain.
In known tensioner designs the chain is over-tensioned in order to ensure that it is sufficiently tensioned when the engine is inoperative and the chain is therefore relatively slack. Over-tensioning increases chain wear and vibration the latter of which increases with engine speed.
The problems of over-tensioning are exacerbated in the case of chain transmissions for driving balance shaft drives or auxiliary chain drives such as those used to drive a water or oil pump or an ignition distributor. In such circumstances the chain may be driven at a speed higher than that driving the camshaft but, as the reverse torque of the driven sprocket is low, the tension imparted to the chain is only required to be relatively low.